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Scientists in western Canada have long been tracking the extent of the mountain pine beetle. This native insect kills weak and old lodgepole pine trees, thus promoting healthy growth of young forests. In times of drought, beetle populations can spike, spreading to healthy pine trees. Historically, cold winters kept beetle populations under control. A new study published in the journal Nature highlights how climate change is promoting pine beetle outbreaks—and how the outbreaks are contributing to climate change.

Global warming is making winter conditions more suitable for the beetle and allowing it to spread to more northern latitudes and higher elevations. This ongoing beetle infestation is the worst scientists have ever recorded, affecting an area about the size of the state of Alabama.

Dead and decaying pines are now widespread in British Columbia, releasing more carbon into the atmosphere than the live trees can absorb during photosynthesis. The new study, which was led by Natural Resources Canada forest ecologist Werner Kurz, predicts that this positive feedback will continue, ultimately releasing over one billion tons of carbon dioxide to the atmosphere.